High-speed varifocal objective system with five-lens basic objective

ABSTRACT

A varifocal objective system with a relative aperture of 1 : 1.8 and a varifocal ratio of about 11 : 1 consists of a five-lens basic objective and a four-component vario attachment. The lenses of the basic objective are all singlets, the third and fourth lenses being dispersive. The attachment is composed of two axially movable negative components bracketed by two substantially fixed positive components; the first component, which may be limitedly shiftable (in whole or in part) for focusing purposes, includes a negative front lens and three positive singlets; the second compartment consists of two negative doublets; the third component is a meniscus-shaped singlet; and the fourth component consists of two air-spaced positive singlets.

[ Dec. 26, 1972 3,563,636 2/1971Macher........t.......................350/i84 3,486,809 12/1969Macher........ ....350/l84 Primary Examineriohn K. Corbin Attorney-KarlF. Ross [57] ABSTRACT A varifocal objective system with a relativeaperture of l 1.8 and a varifocal ratio of about ll l consists of afive-lens basic objective and a four-component vario attachment. Thelenses of the basic objective are all singlets, the third and fourthlenses being dispersive. The attachment is composed of two axiallymovable negative components bracketed by two substantially fixedpositive components; the first component, which may be limitedlyshiftable (in whole or in part) for focusing purposes, includes anegative front lens and three positive singlets; the second compartmentconsists of two negative doublets; the third component is ameniscus-shaped singlet; and the fourth component consists of twoair-spaced positive singlets.

2 Claims, 2 Drawing Figures Bad Kreuznach(Rhineiand), Germany June 30,1971 Appl. No.: 158,439

OR 39707r32f "f UIIIICU Dill!) Macher [s4] HIGH-SPEED VARIFOCALOBJECTIVE SYSTEM WITH FIVE-LENS BASIC OBJECTIVE [72] inventor: KarlMaeher, bad Kreuznach, Germany [73] Assignee: Joe. Schneider 8: Co.Optiaehe Werke Kreuznacil,

[22] Filed:

[30] Foreign Application Priority Data July l, 1970Germany.....................P 20 32 573.9

[52] U.S. Cl. ...................350/184, 350/186, 350/214 [51]Int.Cl..... ......G02b 15/16 [58] Field 0! Seareh........ ....350/-184[56] References Cited UNITED STATES PATENTS 3,350,155 10/1967 Macher.....350/l84X W? iii V l l 5 i i I (I '11 I! a I! d I! II a 'a m (/1 (/101 II! III u 42 a PATENTED w: 2 1912 V 3. 707. 324 SHEET 2 F 2 KarlMacher' INVENTOR.

BY R s 5 0w Attorney BIG H-SPEED VARIFOCAL OBJECTIVE SYSTEM WITHFIVE-LENS BASIC OBJECTIVE My present invention relates to animprovementin varifocal optical objective systems of the general typedisclosed in my prior U.S. Pat. Nos. 3,486,809, 3,549,235 and 3,563,636.

The objective system described and illustrated in each of these priorpatents is divided into a varifocal front lens group or attachment and arear lens group constituting a basic or fixed-focus objective, the frontattachment having two axially movable negative components bracketed bytwo substantially fixed positive components. The term substantiallyfixed" allows for the possibility that one of these positive components,

especially the one in front, be limitedly adjustable for,

focusing purposes, either in its entirety or in some of its parts.Individual focal lengths f,, f f,,,, f of the several components of thisattachment are so chosen that f is equal to or less than 75 percent off,whereas the absolute value of f exceeds by at least 10 percent theabsolute value of f The systems of U.S. Pat. Nos. 3,486,809 and3,549,235 have a relative aperture of 2:1 and a varifocal range (i.e.,ratio of its maximum and minimum overall focal lengths f, and f,,,,,) ofabout l:l. The system of U.S. Pat. No. 3,563,636 has a relative apertureof 1:1.8 and a varifocal ratio greater than 13:1, yet this improvementis realized at the cost of a more complex design of the first componentwhich in that instant (as well as in U.S. Pat. No. 3,549,235) consistsof six rather than four lens members, one of them a doublet, in lieu ofthe four singlets constituting the corresponding component of U.S. Pat.No. 3,486,809.

The general object of the present invention is to provide an improvedsystem which retains the fourmember construction of the first component,according to U.S. Pat. No. 3,486,809, while providing a relativeaperture of about 1:1.8 and a varifocal ratio greater than :1, withcompact dimensioning and with reduction of residual aberrations to aminimum in all operating positions.

I have found, in accordance with the present invention, that an improvedobjective system of this character can be realized by a change in therelative magnitudes of the individual focal lengths f, -f, 0f thecomponents of the forward lens group or attachment and the individualfocal length fy of the rear lens group or basic objective. Moreparticularly, these five individual focal lengths should havesubstantially the following relative numerical values:

Whereas the axially movable second component of a system according toeach of my three prior patents consists of a forwardly convex negativemeniscus followed by a dispersive triplet, a particularly advantageousembodiment of my present invention utilizes for this component a pair offorwardly convex meniscus-shaped doublets each having a forwardlyconcave, preferably collective cemented surface. This affords afavorable correction of chromatic aberration particularly if the lensesof these two doublets have refractive indices greater than 1.65 and ifthe Abbe numbers of their negative constituents substantially exceed,preferably by at least 20 units, those of the associated positiveconstituents cemented thereto. The axially movable third component canthen be a dispersive singlet, similar to that of U.S. Pat. No.3,563,636, whereas the axially fixed fourth component consists of twoairspaced singlets as in each of my three prior patents.

Another important feature of my invention, further improving thechromatic performance of the objective system, resides in theconstruction of the basic objective as a group of five air-spacedsinglets, the third and the fourth of them negatively refracting, incontrast to the four-member rear lens group of my prior patents whereinthe second member is a negative doublet while the other three membersare positive singlets.

The invention will be described in greater detail with reference to theaccompanying drawing in which:

FIG. 1 diagrammatically illustrates an embodiment of my invention; and

FIG. 2 is a graph showing the relative positions of the two movablecomponents of the adjustable front group of the system of FIG. 1throughout its varifocal range.

The objective system shown in FIG. 1 comprises four components I, II,III and IV, together constituting a varifocal front group, and afive-member rear group V representing a basic or principal objectivefrom which the varifocal group may be detached if desired. Component I,which may be limitedly axially displaceable forfocusing purposes butwill otherwise be considered as fixed, consists of a dispersive frontlens Ll with radii r1, r2 and thickness d1, a first positive singlet L2(radii r3, r4 and thickness d3) separated from lens Ll by an air spaced2 which is less than one-fourth of the individual focal length f, ofcomponent I, a second positive singlet L3 (radii r5, r6 and thicknessd5) separated from singlet L2 by an air space d4, and a third positivesinglet L4 (radii r7, r8 and thickness d7) separated from singlet L3 byan air space d6. A variable air space d8 separates component I from theaxially movable negative component II which consists of a forwardlyconvex meniscus-shaped negative doublet composed of a biconvex lens L5(radii r9, r10 and thickness d9) cemented onto a biconcave lens L6(radii r10, r11 and thickness 110) and, spaced from it by a distance d11, a similar doublet composed of a nearly biconvex lens L7 (radii r12,r13 and thickness dl2) cemented onto a biconcave lens L8 (radii r13, r14and thickness dl3). Another variable air space dl4 intervenes betweencomponent [I and the second axially movable negative component III whichis in the form of a forwardly concave meniscus-shaped singlet L9 (radiir15, r16 and thickness dlS). A thirdvariable air space d16 existsbetween component III and the axially fixed positive component IV whichconsists of two biconvex lenses L10 (radii r17, r18 and thickness (117)and L11 (radii thickness d23. Next, separated from lens L13 by an airspace (124, there is a second lens L14 in the shape of a positivemeniscus of radii r25, r26 and thickness d25. The third lens L15 of thisgroup, divided from lens L14 by anair space d26, is a biconcave singletof radii r27, r28 and thickness d27; it is separated by an air space d28from the fourth lens L16 which is a negative meniscus with radii r29,r30 and thickness d29. A final air space d30 intervenes between lens L16and the fifth lens L17 of the basic objective, i.e., a biconvex singletwith radii r31, r32 and thickness d3l.

The following numerical relationships are desirable from the viewpointof suppression of field curvature, moderate lens diameters (especiallyat the front lens) and relatively large surface radii generallysimplifying the manufacture of the lenses: 1

In the following Table A I have listed representative numerical valuesfor the radii r1 r32 and the thicknesses and separations d1 (131 oflenses L1 L17 (the prism P being listed in that Table as a lens L12 ofinfinite radii r21, r22), based on the same linear units (e.g.,millimeters) as the numerical values of the individual focal lengths f,fy given above together with their refractive indices in and Abbenumbers 11,, based upon the E line of the spectrum, for a system havinga relative aperture of 1:1.8, a minimum overall focal length f, of 7.1units, a maximum overall focal length f, of units and a back-focallength of 13.3 units. The variable air spaces d8, dl4 and dl6 are givenfor an intermediate focal length of 32 units.

" TABLEA Thicknesses Lenses Radii Separations n d2 =2.30 air spacer3+214.30 L2 d3-8.10 1.62286 60.08

r4=-92.94 I d4 =0,01 air space r5=+90.24 L3 d5 6.80 1.62286 60.08

. d6=0.01 air space r7=-+49.96 L4 d7 =5.40 1.68083 54.93

r8=+100.30 d d8= 30.23 air space (variable) r9 =+160.50 -L5 d9-4.101.76167 27.37

d10 1.00 1.68083 54.93 r1 11-2160 ll 1 L6 d1 l =4.10 air space 3r12='-279.40 L7 d12 -3.10 1.76167 27.37

r13--34.09 L8 d13'1.00 1.68083 54.93

d14=3.10 air space (variable) r15=17.16 111 L9 d15=1.00 1.48914 70.22

r16=-l74.55 d16=l4.37 air space (variable) r17 =-+120.20 L10 d17==1.801.52583 51.22

r1854.39 1V d18=0.01 air space r19=+48.91 L11 d19=1.80 1.52583 51.22

r20 w d202.80 air space r2l= P L12 I d21-9.00 1.51872 63.96

d22=4.50 air space r23=+21.05 L13 d23=2.85 1.64129 55.15

d24-0.01 air space r25= H 3.36 L14 d25=-2.40 1.69401 54.48

d26=l.40 air space r27-77.08 V L15 d27=1.00 1.81265 25.24

dbl-21.39

I d28=-2.30 air space r29+78.39 L16 d29-1.00 1.81265 25.24

d30-2.00 air space r31=+21.12 L17 d31= 2.45 1.67341 46.82

The exact numerical values of the individual focal length of components1 V in the foregoing system are as follows:

FIG. 2 illustrates the law of motion for the two negative components 11and 111, as represented by the variation of the three air spaces d8, dl4and dl6 always adding up to 47.7 units. Table B, below, gives thenumerical values of these variable air spaces for five distinctpositions of components 11 and 111, with f representing.

the overall focal length.

It will be noted that all the five lenses of the basic objective V havea relatively high index of refractivity, not 0 less than 1.64, ascompared with the indices of the last two components 111, IV of thefront attachment and the intervening prism P.

ln view of allowable tolerances, the decimals given in the first, secondand fourth columns of Table A may be disregarded except in the case ofthe smaller air spaces and lens thicknesses. In the third column, onlythe first two decimals of the refractive indices are consideredsignificant. i

More particularly, the intracomponent spacings could deviate from thelist of values within the following limits:

d2 b 0.03f, to +0.1

d4 by +0.05 f,

d6 by +0.05 f,

dll by 0.1f,, to +0.2f

dl8 by +0.1 f

d26 by -0.03 f to +0.0s

42s by 10.05

By the same token, the planar surface represented by radius r20 could bereplaced by a concave or convex surface of large radius of curvature.

Finally, any compound lens included in the system may be split into itsconstituent lenses separated by a very small air gap.

lclaim:

1. In an optical objective system including a fixedfocus rear lensgroup, the combination therewith of a forward lens group consisting of asubstantially fixed positive first component, an axially movablenegative second component, an axially movable negative third componentand a fixed positive fourth component; said first component includingthree air-spaced collective lens members and a dispersive front lenspreceding said collective lens members, said second component consistingof two air-spaced dispersive lens members; said second and thirdcomponents being displaceable between two extreme positions in which theoverall focal length of the system assumes respective values f,,,,,, andf, defining the lower and upper limits of a varifocal range; said frontlens and said three collective lens members being single lenses L1, L2,L3, L4; the dispersive lens members of said second component being apair of doublets composed of lenses L5, L6 and L7, L8; said thirdcomponent being a single lens L9; and said fourth component consistingof two air-spaced single lenses L10, L11; the numerical values of theradii r1 to r20 and of the thicknesses and separations 111 to d 19 ofsaid lenses L1 to L11, along with their refractive indices n, and theirAbbe numbers 11,, beins substantially as given in the following table:

Rudii 'l'hicltnesles and Separation: n, v, r1 1 20 d] I 2.0 1.79 26 r2=+166 d2 2.3 air space r3 214 d3 8.1 1.02

d4 0.01 air space r5 I d5 6.8 1.62 60 d6 0.01 air space r7 I 50 d8 30air space (variable) '9 161 dll 4.1 air space r12 2.80

dl2 3.1 1.76 27 r13 34 dl3 1.0 1.68 55 r14 II 25 d14= 3.1 air space(variable) r15 17 r16 14 air space (variable) r17 41a 0.01 air space r1949 2. ln an optical objective system including a fixedfocus rear lensgroup, the combination therewith of a forward lens group consisting of asubstantially fixed positive first component, an axially movablenegative.

second component, an axially movable negative third component and afixed positive fourth component; said first component including threeair-spaced collective lens members and a dispersive front lens precedingsaid collective lens members; said second component consisting of twoair-spaced dispersive lens members; said second and third componentsbeing displaceable between two extreme positions in which the overallfocal length of the system assumes respective valuesthe following table:

Thicknesses and Radii Separations r23 +-2l d26 =1.4 r27 77 w air spaceair space air space air space

1. In an optical objective system including a fixed-focus rear lensgroup, the combination therewith of a forward lens group consisting of asubstantially fixed positive first component, an axially movablenegative second component, an axially movable negative third componentand a fixed positive fourth component; said first component includingthree air-spaced collective lens members and a dispersive front lenspreceding said collective lens members, said second component consistingof two air-spaced dispersive lens members; said second and thirdcomponents being displaceable between two extreme positions in which theoverall focal length of the system assumes respective values fmin andfmax defining the lower and upper limits of a varifocal range; saidfront lens and said three collective lens members being single lensesL1, L2, L3, L4; the dispersive lens members of said second componentbeing a pair of doublets composed of lenses L5, L6 and L7, L8; saidthird component being a single lens L9; and said fourth componentconsisting of two air-spaced single lenses L10, L11; the numericalvalues of the radii r1 to r20 and of the thicknesses and separations d1to d19 of said lenses L1 to L11, along with their refractive indices neand their Abbe numbers Nu e, beins substantially as given in thefollowing table: Radii Thicknesses and Separations ne Nu e r1 - 120 d12.0 1.79 26 r2 +166 d2 2.3 air space r3 + 214 d3 8.1 1.62 60 r4 - 93 d40.01 air space r5 + 90 d5 6.8 1.62 60 d6 0.01 air space r7 + 50 d7 5.41.68 55 r8 +100 d8 30 air space (variable) r9 +161 d9 4.1 1.76 27 r10 -65 d10 1.1 1.68 55 r11 + 24 d11 4.1 air space r12 - 2.80 d12 3.1 1.76 27r13 - 34 d13 1.0 1.68 55 r14 + 25 d14 3.1 air space (variable) r15 - 17d15 1.0 1.49 70 r16 - 175 r16 14 air space (variable) r17 + 120 d17 1.81.53 51 r18 - 54 d18 0.01 air space r19 + 49 d19 1.8 1.53 51 r20infinity
 2. In an optical objective system including a fixed-focus rearlens group, the combination therewith of a forward lens group consistingof a substantially fixed positive first component, an axially movablenegative second component, an axially movable negative third componentand a fixed positive fourth component; said first component includingthree air-spaced collective lens members and a dispersive front lenspreceding said collective lens members; said second component consistingof two air-spaced dispersive lens members; said second and thirdcomponents being displaceable between two extreme positions in which theoverall focal length of the system assumes respective values fmin andfmax defining the lower and upper limits of a varifocal range; said rearlens group consisting of five air-spaced singlets including a positivefirst lens L13, a positive second lens L14, a negative third lens L15, anegative fourth lens L16 and a positive fifth lens L17; the numericalvalues of the radii r23 to r32 and of the thicknesses and separationsd23 to d31 of said lenses L13 to L17, along with their refractiveindices ne and their Abbe numbers Nu e, being substantially as given inthe following table: Thicknesses and Radii Separations ne Nu e r23 +21d23 2.9 1.64 55 r24 -132 d24 0.01 air space r25 + 13 d25 2.4 1.69 54r26 + 47 d26 1.4 air space r27 - 77 d27 1.0 1.81 25 r28 + 21 d28 2.3 airspace r29 + 78 d29 1.0 1.81 25 r30 + 10 d30 2.0 air space r31 + 21 d312.5 1.67 47 r32 - 15